1. Field of the Invention
The present invention is related to a cell search method in a mobile communication system, and more particularly, to a cell search method in an asynchronous mobile communication network suitable for reducing a hardware complexity and a power consumption of a mobile terminal by improving a cell search method suggested to ETSI(European Telecommunications Standards Institute) presently.
2. Background of the Related Art
Depending on methods for transmitting a synchronizing signal from a base station to each mobile terminal, the next generation mobile communication network under development(IMT-2000) presently may be sorted as a synchronous mobile communication network and an asynchronous mobile communication network. Standardization of the synchronous mobile communication network is carried out centered on the U.S.A, while the asynchronous mobile communication network is carried out centered on the Europe.
In the asynchronous mobile communication network, when a mobile terminal MT is turned on at an initial state, the mobile terminal should select one base station from a plurality of base stations around the mobile terminal, which can support the best communication service to the mobile terminal as soon as possible. To do this, the mobile terminal receives all synchronizing signal available at first to establish a synchronization with each of the base stations which transmit the synchronization signals, that is call an initial cell search in technical words. During the cell search, each mobile terminal searches for a cell and determines the downlink scrambling code and frame synchronization of corresponding cell. The cell search is typically carried out in three steps as described in the technical specification(TS S1.01 v2.0.0(1999-04)).
During the first step of the cell search procedure, the mobile terminal(MT) uses the SCH's primary synchronization code to acquire slot synchronization to a cell. This is typically done with a single matched filter(or any similar device) matched to the primary synchronization code which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output.
During the second step of the cell search procedure, the MT uses the SCH's secondary synchronization code to find a frame synchronization and identify the code group of the cell found in the first step. This is done by correlating the received signal with all possible secondary synchronization code sequences, and identifying the maximum correlation value. Since the cycle shifts of the sequences are unique the code group as well as the frame synchronization is determined.
During the third and last step of the cell search procedure, the MT determines the exact primary scrambling code by the found cell. The primary scrambling code is typically identified through symbol by symbol correlation over the primary CCPCH(Common Control Physical Channel) can be detected, super-frame synchronization can be acquired and the system and cell specific BCH(Broadcast channel) information can be read.
Such a cell search procedure is carried out by a cell searcher provided to the mobile terminal, wherein, in order to carry out the third step, 16 correlators are used in correlating in parallel. That is, 16 synchronization code which belong to a code group detected in the second step are provided to the 16 correlators respectively, to execute correlation in symbol units. Of course, the cell searcher may be provided with, not the 16 correlators, but one correlator, to execute the correlation in series. However, in this case, the total correlation time period takes a too long time period in comparison to the parallel method, which is not practicable.
However, many users prefer a mobile terminal which, in view of functions, can make fast processing of information and provide a variety of functions, consumes less power, and, in view of shape, has a smaller size and is thinner. Under these communication environment, the cell searcher and the cell search method of the related art mobile terminal have limitations in reducing hardware basis complexity and a power consumption of a channel which provides a synchronization signal.